This invention relates to polynitro aromatic compounds and more particularly to thermally stable polynitro aromatic explosive compounds.
2,5-Dipicryl-1,3,4-oxadiazole is thermally stable in the vicinity of 260.degree. C. and has an impact sensitivity of 20 cm as measured by an ERL machine (2.5 Kg weight, type 12 tools on sandpaper). This combination of impact sensitivity and thermal stability is unique. Comparing 2,5-dipicryl-1,3,4-oxadiazole with its nearest competitors (see table 1) shows that 2,2',4,4',6,6'-hexanitrostilbene (HNS) and 2,2',2",4,4',4",6,6',6"-nonanitroterphenyl (NONA) have similar thermal stabilities but are not as impact sensitive. 2,5-dipicryl-3,4-dinitrofuran has a similar impact sensitivity to 2,5-dipicryl-1,3,4-oxadiazole but it is not as thermally stable.
Short pulse shock tests (exploding foil) on 2,5-dipicryl-1,3,4-oxadiazole showed that it has a shock sensitivity similar to that of pentaerythritol tetranitrate (PETN) (see Table 2). Moreover, the tests also showed that 2,5-dipicryl-1,3,4-oxadiazole has a very sharp threshold of initiation (that is, it always detonates when stimulated at the required energy level but does not detonate below this level). This is a very desirable property for an initiating explosive.
TABLE 1 ______________________________________ Thermal Stability Impact at 260.degree. C. Sensitivity Explosive cc/g/hr. (2 hr.) (cm) ______________________________________ 2,5-dipicryl-1,3,4- 0.6 20 oxadiazole (recrystallized) NONA 0.5 39 (recrystallized) HNS 0.5 45 (recrystallized) HNS (Grade I) 1.7 40 (not recrystallized) 2,5-dipicryl-3,4- 0.8 at 230.degree. C. 23 dinitrofuran (recrystallized) ______________________________________
TABLE 2 ______________________________________ SHORT PULSE SHOCK TEST Threshold Flyer Explosive Velocity Density Cons. Pressure ______________________________________ PETN, Class 2 2.21 km/sec 1.50 103.4 MPa 2,5-dipicryl-1,3,4- 2.33 km/sec 1.61 103.4 MPa oxadiazole ______________________________________
Because of its high thermal stability and impact sensitivity, 2,5-dipicryl-1,3,4-oxadiazole will be useful in slapper detonators, explosive logic systems, detonation transfer compositions, and electric bridge wire explosives. Moreover, it promises to be useful as a thermally stable initiating explosive for use in perforators for deep oil and gas wells. All that is needed is an efficient, economical process for preparing pure 2,5-dipicryl-1,3,4-oxadiazole.
Sharmin, G. P.; Buzykin, B. I.; and Fassakhov, R. Kh. in U.S.S.R. 233,671 (Cl. C07d), 24 Dec. 1965, Appl. 09 Oct. 1967 (C.A. 70:115162) and in Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 741-743, June, 1977 (C.A. 87:184435) disclose the preparation of 2,5-dipicryl-1,3,4-oxadiazole by refluxing 2 mmol. (1.20 g) of N,N'-bis(2,4,6-trinitrobenzoyl)hydrazine in 100 ml of POCl.sub.3 for 20 hours. The large quantity of POC1.sub.3 required for this procedure makes scale up dangerous and impractical. The long reaction (reflux) time required, the poor yields and impurity of product further make this process impractical for commercial production.
Dacons, Joseph C.; and Sitzmann, Michael E., Journal of Heterocylic Chemistry, 14, 1151-5 (1977) disclose the cyclization of N,N'-bis(2,4,6-trinitrobenzoyl)hydrazine with PCl.sub.5 in nitrobenzene to produce 2,5-dipicryl-1,3,4-oxadiazole in yields of 30-35 percent. Separation of the product 2,5-dipicryl-1,3,4-oxadiazole from nitrobenzene (b.p. 210.degree. C.) is very difficult. The nitrobenzene is removed either by steam distillation or by pouring the nitrobenzene reaction mixture into a second solvent (e.g., methanol) in which 2,5-dipicryl-1,3,4-oxadiazole is much less soluble. However, combining the nitrobenzene with a second solvent makes it quite difficult to recycle the nitrobenzene for further use in the process. In summary, this procedure would be difficult and expensive to scale up for commercial production.
It would therefore be desirable to provide a relatively simple, low cost method of producing 2,5-dipicryl-1,3,4-oxadiazole.